Rapid advances in technology in several areas have converged to enable small, portable memory cards with vast capacities. Flash memory technologies such as those using electrically-erasable programmable read-only memory (EEPROM) have produced chips storing 128 M-Bytes or more. Small flash-memory cards have been designed that have a connector that can plug into a specialized reader, such as for compact-flash, secure-digital, memory stick, or other standardized formats.
More recently, flash memory cards are being sold that contain a USB connector. Such USB-flash memory cards do not require a specialized reader but can be plugged into a USB connector on a host system, such as a personal computer (PC). These USB-flash memory cards can be used in place of floppy disks. A USB-flash card can have a capacity of more than ten floppy disks in an area not much larger than a large postage stamp.
FIG. 20(A) shows a prior-art flash-memory card with a conventional male USB connector. Flash memory chip 12 may be a 128 Mega-byte non-volatile chip or may have some other capacity. Controller chip 14 contains a flash-memory controller that generates signals to access memory locations within flash memory chip 12. Controller chip 14 also contains a USB interface controller that serially transfers data to and from flash memory chip 12 over a USB connection.
Male USB connector 20 is mounted on a board 10, which is a small circuit board with chips 12, 14 mounted thereon. Multi-layer printed-circuit board (PCB) technology can be used for board 10. A plastic case (not shown) can surround board 10.
Male USB connector 20 contains a small connector substrate 16, which is often white ceramic, black rigid plastic, or another sturdy substrate. Connector substrate 16 has four or more metal contacts 18 formed thereon. Metal contacts 18 carry the USB signals generated or received by controller chip 14. USB signals include power, ground, and serial differential data D+, D−.
Male USB connector 20 contains a metal case (plug shell) 11 that wraps around connector substrate 16. The plug shell touches connector substrate 16 on three of the sides of connector substrate 16. The top side of connector substrate 16, holding metal contacts 18, has a large gap to the top of the plug shell. On the top and bottom of this metal wrap are formed holes 15. USB connector 20 is a type-A USB connector.
FIG. 20(B) shows a female USB socket connector 22. Female USB socket connector 22 can be an integral part of a PC or other host system, or can be connected by cable 21 to such a host system. Another connector substrate 26 contains four metal contacts 28 that make electrical contact with the four metal contacts 18 of the male USB connector 20 of FIG. 20(A). Connector substrate 26 is wrapped by a metal case, but small gaps are between the metal case and connector substrate 26 on the lower three sides.
Locking is provided by metal springs 24 in the top and bottom of the metal plug shell. When male USB connector 20 of FIG. 20(A) is flipped over and inserted into female USB socket connector 22 of FIG. 20(B), metal springs 24 lock into holes 15 of male USB connector 20.
FIGS. 21(A) and 21(B) are cross-sections highlighting connections between male and female USB connectors. Female USB socket connector 22 is on the left while male USB connector 20 is being inserted from the right. Male USB connector 20 is flipped over relative to the view of FIG. 20(A). Metal contacts 18 are formed on the lower surface of connector substrate 16 on male USB connector 20, while metal contacts 28 are formed on the upper surface of connector substrate 26 on female USB socket connector 22. Thus the metal contacts face one another to allow for electrical contact when male USB connector 20 is inserted into female USB socket connector 22 as shown in FIG. 21(B).
Metal springs 24 formed on the metal case surrounding connector substrate 26 on female USB socket connector 22 fit into holes on the plug shell of male USB connector 20. This helps to lock the connectors together.
A problem associated with the production of conventional male USB devices that utilize standard male USB plug connectors typically require lead-based soldering methods to attach the standard plug structure (e.g., substrate 16 and plug shell 11) to circuit board 10. Lead (Pb) is recognized as a hazardous material, and may at some point in time be banned from use. Lead-free soldering requires higher peak temperatures (about 240° C.) that can shrink or warp plastic substrates, thereby making such conventional USB plug connector structures unsuitable for lead-free fabrication processes.
FIG. 22 shows a prior-art USB flash memory card using a low-profile USB connector that avoids the need for attaching a separate substrate and plug shell to a circuit board by integrating male USB connector 30 with board 32, and by omitting the plug shell entirely. Board 32 is a PCB that has flash memory chip 12 and controller chip 14 mounted on the upper surface thereof (i.e., on the same surface as contacts 38). Board 32 is extended to include male USB connector 30, which has metal contacts 38 formed on end 36 of board 32. The width and thickness of board 32 at end 36 containing male USB connector 30 is designed to approximately match that of connector substrate 16 of FIG. 20(A). Plastic case 34 can enclose board 32 but have an opening for metal contacts 38. Plastic case 34 can cover the bottom and sides of male USB connector 30 up to end 36 to emulate portions of the metal case of the male USB connector of FIG. 20(A).
FIGS. 23(A) and 23(B) show cross-sections of the prior-art lower-profile USB connector being inserted into a standard female USB connector. Board 32 that has male USB connector 30 formed on end 36 is flipped over from the view shown in FIG. 22, and end 36 is inserted into female USB socket connector 22 from the right side.
Metal contacts 38 are located on the lower surface of male USB connector 30. Plastic case 34 has an opening on the lower surface of male USB connector 30 to expose the metal contacts so they can make electrical connection with metal contacts 28 on the upper surface of connector substrate 26 of female USB socket connector 22 when inserted as shown in FIG. 23(B).
Plastic case 34 helps to fill the gate between board 32 and the top edge of the metal case of female USB socket connector 22. However, no holes are provided in plastic case 34, so metal springs 24 are pushed up slightly when male USB connector 30 is inserted into female USB socket connector 22. Plastic case 34 is also formed along the thin edges of board 32 and helps to fill in the gaps between connector substrate 26 and the sides of the metal case of female USB socket connector 22 that are above and below the plane of FIG. 23(B).
While USB connector 30 can be less expensive and smaller than the standard USB connector and avoids the need for plug shell, it can have the undesirable characteristic of wobbling in the female USB connector socket, and exposes contacts 38 to damage.
What is needed is a reduced length USB device having a male USB connector plug that avoids the need for soldering the plug shell to the circuit board.